Method of producing anticorrosion high tensile strength rail



United States Patent Ofiice Patented Dec. 6, 1966 3 290 183 a METHOD or rnonucirso ANTICORROSION men I TENSILE STRENGTH RAIL Tadashi Ohtake, Tohata, Fukuoka; Koichi Aoki, Yawata,

temperatures. The chromium content in the rail of the present invention is about 2.0 to 6.0% to give corrosionresistance and strength. When the chromium content is less than about 2%, there is very little corrosion- Fuklwka, and 1530 Kimura, Tobfiia, Fukuoka, Japan, 5 resistance. When it is more than about 6%, corrosion- $0 zf 3 81 Steel n -i resistance does not increase sufficiently to make the rail a P l' 0 economical. Mol bdenum eatl irn roves both strength Claims Prmmy applecaimn Japan 1961 and toughness. hi the prese rit 15365555, the molybdenum N Drawing. Filed Aiig. 21, 1962, Ser. No. 218,429 content is less than about 1% or preferably about 0.1 to 3 Chime (CL 14g 12 0 0.4%. Less than about 1.0% of each of nickel, vanadium, boron, copper, titanium and niobium may be added to The inventi'en relates to method for Pmd'ucmg Corro increase the strength and toughness or corrosion-resistance sion-resistant high tensile strength rails. but they are not necessary ingredieme Rails aemany'used in every P Y today "i largely Ln producing the rail of the present invention, a steel Classified with respect to their Composltlons as high f 15 ingot having the above composition is bloomed, is then steel rails and low carbon medium manganese steel rails. slowly Cooled is heheated and is then mhed into a rail In Japan, most of the rails are carbon steel rails which and the rail is then Cooled at a properlyeemmned eeehng are intermediate between the above mentioned two kinds. rate or the rail eeeled to room temperatm-e is then In some parts of Europe and America, rails containing tempered very small amounts of Cr and V or Si-Mn series h Y When the rail of the present invention is rolled and been .eXPeTimemauY manufactured In order is then cooled in air, the hardening rate is so great that fatigueresistance or high tensile strengths However, these the rail becomes very m m Further because f h rails contain only small amounts of alloys and are not hairs Strong tendency to flake the finishrehed rail is intended to have corrosion-resistance. In carbon steel slowly .eoeled to obtain toughness and to prevent the rails used today, the amount of breaks due to both c r -Q- mation of flakes. By such heat-treatment, the formation Sion and fatigue and due cormslon and electrolytic of flakes is prevented, toughness is attained and, at the Corrosion are Very highon the other hand the fatlgue same time, corrosion and fatigue-resistance are increased. limit of current carbon steel rails is to kg./nrm. POT vSuch h .t t m f after mining the mil, it is But, in old rails which have been used to some extent, f bl to p the rail into, a h keeping .fumaee or the fatigue limit decreases due to their exposure to cor- 30 a soaking hit e the temperawfe of the nail has roding environments. Current rails are not yet satisreached about 750 to Qdurihg the aipeeeh'ng The factory with respect Corrosion fatigue-resistance rail is slowly cooled therein for more than about 7 hours Object the Present inventlon 15 completely to about 200 to 150 C. The rail can thereafter be air eliminate the defects of conventional rails with respect to cooled to mom vtermyermure ft the finish 1 then corrosion and fatigueresistance and to provide rails hav- 35 tempered at about 400 t 800 C. and again air-cooled. ing high Corrosion and fatigue'fesieta'nee- By this procedure, rails high in conr-osi-omresistance,

Another object of the present invention is to give toughtoughness and f tj i t are obtained ness and anticorrosion to rolled rails and to provide rails Blooming er Lrolling f rails can be Tehlaeed other in which the Production of flakes is preventedprocesses such as, for example, pressing, extrusion or The rail according to the present invention is composed 4O fo i Of about t0 0., about t-O CI, less Table 1 show thehemical compnsitions of a corrothan about 10% less fihan about less than sion-resistant high tensile strength rail according to the about 10% Si and the remainder being Fe and unavoidpresent invention and of a current carbon steel rail. able impurities and y eiPeumSlianees, Table 2 shows the results of tests conducted with the contain less than about 1.0% Ni, less than about 0.5 V, id n less than about 1.0% Cu, less than about 0.01% B, less than about 0.5% Ti and/or less than about 0.5 Nb. Table 1 In the rail of the present invention, high toughness and corrosion-resistance are achieved by properly controlling C Si Mn P 8 Cr M0 the cooling rate of the rail after rolling it, or by tempering 5 the rail after cooling to room temperature. Ra f th present The rail according to the present invention can contain g' f lfi e e carbon in a range of about 0.25 to 0.05% in view of its rail 0.65 0.13 0.81 0.014 0.025 self-hardenability and the precipitation of carbide at high Table 2 V-notch Charpy value Rotary bending fatigue Corrosion in mm./ 111 kg.-rn./cm. limit in kgjmm. half year Yield Tensile Elcnga- Reduc- Hardpoirtin strength tion in tion of ness in Room Smooth, Sprayed lag/mm. in Percent area in Brinell tempera- 20 C. Smooth With corroded Exposed with kg./mm. Percent ture notch with outdoors salt water water L o L 0 Hail of the present invention 76.8 130.6 11.6 20.9 374 8.12 3.89 6.52 3. 51 55.0 28.0 31.0 0.022 0.55 Current carbon steel rail 43.3 87.5 13.8 23.5 249 1.30 0.65 32.0 15.0 20.0 0.078 0.

Table 3 Air-cooled to Air-cooled to Slow cooling from each temperature during air cooling after finish-rolling the room term the room temerature after peratuer after a o oing directly being reheated 500 0. 550 O. 600' O. 650 C. 700 O. 150 0.

fed and rolled and rolled Tensile strength in kg./mm. 122.4 135.0 133 .1 133 .3 132.9 134.0 133 .8 134.1 Elongation in percent 2.3 5.8 6.7 7.6 9.9 13.0 11.8 11.9 Reduction of area in percent 4.7 8 .7 12.8 14.5 19 .9 25 .2 28 .7 28 .3 V-notch Charpy value in kg.-n1 /cm 2 7 .2 7 .7 7 .8 7 .7 7 .8 8 .1 8 .1 8 .2 Hardness in Brinell 385 382 376 375 373 372 363 367 As apparent from these result-s, as compared with the current carbon steel rail, the corrosion-resistant high tensile strength rail of the present invention has a yield point, tensile strength and fatigue limit 1.5 to 1.8 times as high, an elongation and reduction of area not substantially different, an impact value several times as high and a much higher low-temperature impact value. On the other hand, the corrosion-resistance of the rail of the present invention is more than three times as high. In the process for producing rails according to the present invention, reheating after blooming and slow cooling treatments after the finish-rolling are the most essential conditions. These operations improve the elongation and reduction of area values. Current carbon steel rails are not affected by reheating and slow cooling. That is, current rails have substantially the same mechanical properties When slowly cooled to room temperature after being rolled as they do when they are not slowly cooled. Therefore, with reference to Tables 2 and 3, as compared with current carbon steel rails under the same conditions, i.e. slowly cooled to room temperature after being rolled, the rail of the present invention has a much higher tensile strength and hardness but is lower in elongation and reduction of area. It is therefore evident, that according to the present invention, a very high tensile strength is obtained, hardness and strength are not altered or are higher, the rates of elongation and reduction of area are equal to those of current carbon steel rails, and high corrosion-resistance is attained. Further, it is seen in Table 3 that the elongation and reduction of area of the rail of the present invention are more improved by reheating before rolling than by directly [rolling and are further improved by slow cooling from 500 to 750 C. after finishrolling.

What we claim is:

1. A method of manufacturing steel rail which is high in tensile strength and anti-corrosiveness which comprises subjecting a steel containing from 0.05 to 0.25% carbon, from 2.0 to 6.0% chromium, trom about 0.10% to less than 1.0% molybdenum, less than 1.0 silicon, and less than 1.5% manganese to a blooming rolling, cooling the rolled steel down to a temperature below the A transformation point of the steel, again heating said steel up to a rolling temperature, at which temperature said steel is rolled in rail, and the-n gradually cooling said rail from a temperature above 500 to 700 C. down to 150 C., over a period in excess of 7 hours.

2. A method as in claim 1, in which a mixture of elements selected from a group consisting of less than 1.0% nickel, less than 0.5% vanadium, less than 1.0% copper, less than 0.01% boron, less than 0.5% titanium and [less than 0.5% niobium are added to the main components of the steel.

3. A method of manufacturing steel rail which is high in tensile strength and anti-corrosiveness which comprises subjecting a steel containing from 0.05 to 0.25% carbon, from 2.0 to 6.0% chromium, less than 1.5% manganese, from 0.1 to 1.0% molybdenum and less than 1.0% silicon as main components, adding an element selected from a group consisting of less than 1.0% nickel, less than 0.5% vanadium, less than 0.5 niobium, less than 1.0% copper, less than 0.01% boron, less than 0.5% titanium, and mixture thereof and the rest being Fe, to a blooming rolling, subjecting the bloomed material to a finishrollin-g, to rail, subjecting the trail to an air-cooling after the finishrolling, putting the rail into a heat-keeping furnace, when the temperature of the rail becomes 500 to 750 C., in which the rail is gradually cooled from a range of 500 to 750 C. down to a range of 150 to 200 C. for more than 7 hours.

References Cited by the Examiner UNITED STATES PATENTS 1,277,372 9/1918 Birunner 148l2 1,721,555 7/1929 Hamilton et a1. l26 1,925,029 8/1933 Brunner 14812 FOREIGN PATENTS 797,762 2/1936 France.

324,686 1/1930 Great Britain.

340,819 1/1930 Great Britain.

517,118 1/ 1940 Great Britain.

731,684 6/1955 Great Britain.

DAVID L. RECK, Primary Examiner. P. WEINSTEIN, Assistant Examiner. 

1. A METHOD OF MANUFACTURING STEEL RAIL WHICH IS HIGH IN TENSILE STRENGTH AND ANTI-CORROSIVENESS WHICH COMLESS THAN 1.0% MOLYBDENUM, LESS THAN 1.0 SILICON, AND LESS THAN 1.5% MENGANESE TO A BLOOMING ROLLING, COOLING PRISES SUBJECTING A STEEL CONTAINING FROM 0.05 TO 0.25% CARBON, FROM 2.0 TO 6.0% CHROMIUM, FROM ABOUT 0.10% TO THE ROLLED STEEL DOWN TO A TEMPERATURE BELOW THE A1 TRANSFORMATION POINT OF THE STEEL, AGAIN HEATING SAID STEEL UP TO A ROLLING TEMPERATURE, AT WHICH TEMPERATURE SAID STEEL IS ROLLED IN RAIL, AND THEN GRADUALLY COOLING SAID RAIL FROM A TEMPERATURE ABOVE 500 TO 700*C. DOWN TO 150*C., OVER A PERIOD IN EXCESS OF 7 HOURS. 